WDM Router

ABSTRACT

The present invention provides a mixed analog and digital chip-scale reconfigurable WDM network. The network suitably includes a router that enables rapidly configurable wavelength selective routers of fiber optic data. The router suitably incorporates photonic wavelength selective optical add/drop filters and multiplexers.

PRIORITY CLAIM

This application claims priority from the U.S. provisional patentapplication Ser. No. 60/404,073 entitled “Mixed Analog And DigitalChip-Scale Reconfigurable WDM Network” and filed on Aug. 15, 2002,contents of which are incorporated by this reference.

FIELD OF THE INVENTION

This invention relates generally to fiber optic communication and, morespecifically, to routing optic signals on a fiber optic network.

BACKGROUND OF THE INVENTION

Most information systems, such as personal computers and automotivecontrolling computers, rely upon a copper wire based network to carrysignals to remote components. In many ways, this has proven to be animpediment to the speed of the system. At the center of a computer, forinstance, a Pentium 4 central processor might operate at 2.4 GHz, butdata travels on a central bus on a circuit board at a mere 400 MHz,while output devices might only receive their instructions at 133 MHz.

One approach is to push the wire to its theoretical limits. Physicaldimensions, such as length and diameter, and the parasitic resistance,capacitance, and impedance resulting from the dimensions, however,define a wire. At low frequencies or bit rates, the series resistanceand shunt capacitance of the wire (or circuit board trace) dominate itsbehavior. The rise or fall time limits the data rate. As the designerchooses to push the frequency higher, the wire's own impedance becomesthe dominant factor, acting much as transmission lines to attenuate andreflect signals based upon the characteristic impedance of the lines.The fastest processor ends up waiting for the wires.

In high performance communication systems, photons have supplantedelectrons as messengers. Photons travel on fiber optic waveguides fromplace to place at the speed of light. The photon frees the processorfrom its copper shackles. The market is just starting to see the severalcomponent-based optical networks capable of transmission rates of 2.5Gb/sec. Chip-to-chip fiber optic connections could boost the output of aprocessor by a factor of a thousand.

One natural application for such a fiber optic network is militaryfighter aircraft. For the last century, the military has sought tointegrate the latest technologies into the field of battle as a means ofmultiplying its strength. A modern fighter aircraft is effective becauseof the amazing array of computers, sensors, triggers, and displaysonboard. The fighter is not only an airplane but it is also acombatant's instrument. In that role, it must defend itself, reconnoiterthe theater of operations, track targets, jam enemy sensors, and fireits weapons. Because the weapons, themselves, are “smart,” the aircraftoften must be competent to converse with the weapons in order to chargethem with their mission before and during flight.

Not only is the aircraft an array of computers, but also among the arrayof computers, there exists, on the airframe, a great variety ofcomputers. Some threat computers receive analog input—digitizing wouldslow reaction to the threat. Some engine sensors send analog informationonly. An optical network ideally should be able to handle both in orderto be fully effective in optimizing the communication within theairframe.

Analog systems differ from digital systems. When transmitted over anoptic fiber, analog and digital systems differ greatly in magnitude. Allnetwork systems have ambient noise. In an analog system, the approach tofidelity over ambient noise is to “shout” over it. Where an analogsystem has an anticipated range of values, the maximum value is set at again value representing the near maximum capacity of the fiber. Theminimum value is designated as the first value reliably discernable overthe noise. That value then becomes the bias for the analog systemallowing fidelity in all information transmitted.

Digital systems have a slightly different approach to noise. Using thesame ambient level as a threshold, only the “ones” have to exceed theambient. The “zeros” can be buried in the noise without ill effect. Insome systems where the “zeros” must emerge from the noise for the sakeof timing, values for “zero” and “one” are set such that both exceed thenoise but still do not approach magnitude of the analog signal. These,too, are “whispers” compared to the analog “shout.”

Systems within a fighter airframe are located at discrete places thatallow optimal performance of the system. For instance, a wing might holda variety of sensors: feedback loops for aileron and flap positions,anti-stall sensors, threat assessment antennae, fuel state sensors, andweapons state nodes. The information from each of the sensors mustultimately get to distinct systems on the airframe for processing.

One means of getting the information on the system has been to assign itto discrete optical “channels” according to the intended destination. Byconvention, the military has decided to designate 32 such channels forboth analog and digital signals. The channels are partitioned to each oftwo common wavelength bands: 1.55 μm for analog signals and 1.3 μm fordigital signals. Each of the channels has a rate capacity ofapproximately 2.5-40 Gb/second. Information senders are assigned towavelengths according to the receiving system and according to thenature of the output, i.e. digital or analog.

Wavelength division multiplexing (WDM) is the process of carrying lightof multiple wavelengths within the fiber. The fiber will carry theseveral channels without interference. WDM combines multiple opticalsignals so that they can be amplified as a group and transported over asingle fiber to increase capacity. At the receiving end of the fiber,the information carried on the several channels is taken off of thefiber and separated into its several channels and recombined based upondestination.

Such a system presumes the existence of a router capable of sensing thewavelength of a channel carrier (arbitrarily λ₁) from a WDM transmitterat a source and capable of placing the information from the designatedchannel onto the correct optic trunk to reach the intended WDM receiverdestination in the system. Optical channels are separated and recombinedmost readily through the phenomena known as refraction and diffraction.Refraction is the deflection from a straight path undergone by a lightray or energy wave in passing obliquely from one medium (such as air)into another (such as glass) in which its velocity is different.Diffraction is a modification that light undergoes in passing by theedges of opaque bodies or through narrow slits or in being reflectedfrom ruled surfaces and in which the rays appear to be deflected and toproduce fringes of parallel light and dark or colored bands. In eitherregard, the light waves are bent according to their wavelength.

Many WDM multiplexers and de-multiplexers in current use, such asarrayed waveguide gratings (AWGs), are complex to fabricate, bulky insize, and relatively costly. The AWG consists of a number of arrayedchannel waveguides that act together like a diffraction grating in aspectrometer. The grating offers high wavelength resolution, thusattaining narrow wavelength channel spacings such as 0.8 nm. Otherde-multiplexers include traditional dispersive devices, such asdiffraction gratings and prisms. While being much simpler and lessexpensive than AWGs, these devices typically have an angular dispersionless than one degree per nm, which prevents them from being sufficientlycompact for most applications. Regardless of the configuration, becauseof their dependence on geometry, the routers are very sensitive totemperature and generally to shock, thus not well-suited to a militaryenvironment.

Superprisms, a much more highly dispersive photonic crystal counterpartto the array waveguide (AWG), have been used to map differentwavelengths onto different propagation paths. Superprisms are simplerand much smaller than AWGs, and have very low cross-talk. They are aspecial type of photonic crystal de-multiplexing structure that providesangular separation by wavelength that is up to 100 times the angularseparation of conventional dispersive media.

Photonic crystals are optical materials with an intricatethree-dimensional structure that manipulates light in unusual waysthanks to multiple Bragg diffraction in specific directions. Thestructure has the length scale of the order of the wavelength of light.An example of a photonic crystal is the gem opal, which consists of aregular array of tiny silicate spheres, ordered like the atoms in acrystal lattice, but on a scale a thousand times larger. If thestructure has a large enough variation in refractive index for aperiodic array of holes or columns in specific directions relative tothe symmetry of a crystal lattice, a “photonic bandgap” occurs. Underthese special circumstances, Bragg diffraction prevents a certain rangeof wavelengths from propagating in selected directions inside thecrystal. By designing the bandgap appropriately, i.e. by engineering thelattice spacing of the photonic material to be either highly dispersiveor to blocks wavelengths (except those wavelengths passed by controlleddefects, the resulting crystal will function as a superprism withdispersive properties for a superprism being many times greater thanthat of optical glass prisms. Such superprisms can be created by thesame lithographic technologies that are currently employed forconstructing integrated electronic circuitry. Alternately, controlleddefects introduced into photonic crystal lattices can lead to wavelengthselective resonator filters within the photonic band gap.

Currently WDM components occupy a volume or footprint that is too largefor emerging military platforms. In addition, the WDM components willonly support static network topologies, not allowing for new functionsor services. Photonic crystal resonator filter components designed fordigital power levels are expected to destructively overheat under thegreater power outlay of analog systems. Analog systems require highersignal to noise ratios than is required to discern between the powerlevels assigned to “zeros” and “ones.”

What is needed then, is a WDM router on a chip-scale that overcomesproblems with WDM components known in the art.

SUMMARY OF THE INVENTION

The present invention provides a mixed analog and digital chip-scalereconfigurable WDM network. The network suitably includes a router thatenables rapidly configurable wavelength selective routers of fiber opticdata. The router suitably incorporates photonic wavelength selectiveoptical add/drop filters and multiplexers.

Because of the scale and the programmable nature of the router, it couldbe economically be substituted as either a multiplexer or de-multiplexeras well, thereby allowing a smaller inventory to service an existingnetwork.

In one exemplary embodiment, mixed analog and digital chip-scalewavelength selective router includes an optical de-multiplexerassociated with each of a plurality of fiber optic inputs and an opticalmultiplexer associated with each of a plurality of programmable fiberoptic outputs. A programmable resonator filter is associated with eachof a plurality of programmed light wavelengths predesignated as channelsfor carrying digital signals for receiving light from the plurality ofoptical de-multiplexers and in optical communication with theprogrammably associated optical multiplexer. A first programmablesuperprism is associated with each of the light wavelengthspredesignated as channels for carrying analog signals receiving theassociated light wavelength from the plurality of opticalde-multiplexers and directs the associated light wavelength asprogrammed. A second programmable superprism is programmably associatedwith each first programmable superprism and located for receiving thedirected light wavelength and redirecting the directed light to theprogrammably associated optical multiplexer.

In a preferred embodiment, the instant invention presents a photonicintegrated circuit approach to chip scale WDM enabled by a process tomodel, fabricate, and integrate III-V on Silicon, silicon-on-insulator(SOI), and electro-optic polymer technology. A voltage applied to asuitably oriented electro-optic polymer changes the wavelengthdispersion or resonance filter wavelength of the SOI superprism orresonator filter. This leads to compelling wavelength selective devicesthat are rapidly reconfigurable wavelength selective cross-connects forrouters. The high power analog signals are routed by super-dispersiveelements at 1.55 um and tunable filter resonators rout lower powerdigital signals. The resulting tunable wavelength selectivecross-connect elements lead to a wafer scale router capable of routingthe wavelength channels of analog data at 1.55 μm and the wavelengthchannels of digital data at 1.3 μm. Thus, the router matches thewavelength band labeled analog and digital data with the power, size,and wavelength characteristics of the nanophotonic routing device on thechip uniquely tailored to route either high power analog WDM signals orlower power WDM digital data links.

Because of the scale and the programmable nature of the router, it couldbe economically be substituted as either a multiplexer or de-multiplexeras well, thereby allowing a smaller inventory to service an existingnetwork.

According to an aspect of the invention, reversible optical paths areprovided thereby allowing efficient upstream and downstream routing,broadcast and mixing modes.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings.

FIG. 1 is a schematic diagram of chip according to an embodiment of thepresent invention;

FIG. 2 is a schematic diagram contrasting the analog and digitalsections of the router;

FIG. 3 is a band energy graph indicating the energy as a function of thegeometry of the superprism;

FIG. 4 a is a photomicrograph of a placed defect in the superprismcausing resonance;

FIG. 4 b is a photomicrograph of a series of placed defects in thesuperprism causing resonance;

FIG. 5 is a schematic diagram showing the overhead and cutaway views ofa programmable resonator; and

FIG. 6 is a photomicrograph of a programmable resonator.

DETAILED DESCRIPTION OF THE INVENTION

A mixed analog and digital chip-scale wavelength selective routerincludes an optical de-multiplexer associated with each of a pluralityof fiber optic inputs and an optical multiplexer associated with each ofa plurality of programmable fiber optic outputs. A programmableresonator is associated with each of a plurality of programmed lightwavelengths predesignated as channels for carrying digital signals forreceiving light from the plurality of optical de-multiplexers and inoptical communication with the programmably associated opticalmultiplexer. A first programmable superprism is associated with each ofthe light wavelengths predesignated as channels for carrying analogsignals receiving the associated light wavelength from the plurality ofoptical de-multiplexers and directs it as programmed. A secondprogrammable superprism is programmably associated with each firstprogrammable superprism and located for receiving the directed lightwavelength and redirecting to the programmably associated opticalmultiplexer.

FIG. 1 presents an overview of the inventive router on its native chip100. Shown is one of a plurality of inputs 10 attached to the inboundoptical fibers from various sources. Also portrayed are the plurality ofoutputs 20 arranged to send outbound optical signals along opticalfibers to their respective systems. There is no reason why the number ofinputs and the number of outputs must necessarily correspond. Oneskilled in the art will readily appreciate that the variety andlocations of sensors and enunciators might easily define several inputareas for which separate fibers might suitably serve. On the other hand,the number of systems or destinations for the information will dictatethe number of output channels.

Each of the inputs 10 is fed into a superprism de-multiplexer 110 inorder to split generally higher power analog signals from generallylower power digital signals. The reason for de-multiplexing the digitalsignals from the analog signals is to protect the integrity of the chip100 while assuring maximum fidelity for each type of signal. To makeanalog signals readily susceptible to de-multiplexing from the band ofdigital signals, by convention according to an embodiment of theinvention, each type of signal is assigned to one of two bands definedby base wavelengths: about 1.55 μm for analog signals and about 1.3 μmfor digital signals. However, it will be appreciated that other bandsare possible and consistent with this invention.

Once the analog and digital signals are separated at each inputde-multiplexer 110, the digital signals from each input de-multiplexer110 are fed to a superprism digital signal de-multiplexer 112, therebyfurther splitting the digital signal into constituent channels. Again,convention may define the several channels within the digital band. Forexample in one embodiment, one present convention defines 32 channelswithin each band. As distinct channels, the output of the digital signalde-multiplexer 112 is fed into a digital resonator 140 for routingaccording to wavelength. A digital health monitor tap 121 and a digitalsignal injection tap 179 communicate with the digital resonator 140.

The output of the digital resonator 140 is the light output of all ofthe inputs 10 and routed according to wavelength and programmableelectronic inputs (not shown). Each wavelength is collected by asuperprism digital signal multiplexer 188. From the superprism digitalsignal multiplexer 188, the optical information is remultiplexed withanalog output by an output signal multiplexer 190 corresponding to itsoutput 20.

Like the digital band, the analog band is de-multiplexed according towavelength at an analog signal de-multiplexer 115. The output of eachanalog signal de-multiplexer is a series of discrete channels. Ratherthan a resonator, the output at each input de-multiplexer 110 is fedinto a beam steering device 160 to handle the greater power of theanalog signals. Like those of the digital resonator 140, two tapscommunicate with the analog beam steering device 160, the analog healthmonitor tap 125 and the analog signal injection tap 175.

The output of the analog beam steering device 160 is fed into asuperprism analog signal multiplexer 185. The multiplexer 185 isselected according to the wavelength of the analog signal and theprogrammed steering of the beam. From the analog signal multiplexer 185,the signal joins a digital signal at the output signal multiplexer 190corresponding to the output port 20.

The de-multiplexing and the multiplexing tasks are all carried out onthe chip 100, by passive optical elements. Each of the de-multiplexers,110, 112, and 115, and each of the multiplexers, 185, 188, and 190 arepassive superprisms, and carry out their tasks according to refractiveindices and geometric placement. Configuration and manipulation ofconstituent elements of the superprisms and computer aided placement(known as “Wavelength scalable Finite Difference Time Domain (FDTD)optical modeling”) will assist in precise element design, placement andinterworking of these elements.

Referring now to FIG. 2, elements of the chip 100 that are responsive toprogramming are the digital resonator 140 and the analog beam steeringdevice 160. The digital resonator 140 and the analog beam steeringdevice 160, each executes similar functions but is distinctly drivenaccording to the power levels entailed for signal fidelity. Both beamsteering and programmable resonator filters have shown greater levels oftolerance for shock and heat because their construction has improved thequality of the response and the durability of these optical components.For this reason, it is not necessarily the case that while operating atdistinct wavelengths, the two chambers must be distinctly driven. Forexample, the chip 100 with two beam steering devices for both analog anddigital signals may include two resonators as described. By configuringthe chip 100 with both technologies in a presently preferred embodiment,both are enabled.

The digital resonator 140 relies upon resonators to sort wavelengths.Once light of an appropriate wavelength is captured in the resonator,waveguides usher the light to its prescribed output from the resonator140. One presently preferred embodiment employs micro-resonators in theform of rings, disks, or photonic crystals as the building blocks thatprovide the key functions of wavelength filtering and routing. Inpractical systems, it is advantageous to make these resonators active orprogrammable in order to correct for minor process or designimperfections and to allow control of the resonator characteristics. Inone presently preferred embodiment, this control is acheived througheither tuning Q of a III-V compound semiconductor resonator (orresonance tuning of an SOI resonator) by altering optical loss (or gain)within the resonator (or tuning its resonance wavelength by changing therefractive index of the ring or photonic crystal element to change theeffective cavity length of the resonator). In a micro-ring resonator, acompound semiconductor structure containing an optically active layer isgrown on top of the passive ring waveguide. The evanescent optical fieldof the ring waveguide overlaps the active layer allowing interactionwith the resonant optical mode via photon absorption or emission. Theamount of loss (or gain) in the resonator, and therefore its Q as well,is then determined by the number of photons coupled into or out of theresonant mode via the active layer. External control of the active layeremission is achieved through electrical biasing of a p-n junction(forming a light emitting diode), or by optical pumping at an absorptivewavelength sufficiently removed from the signal channels. The physicalconfiguration of these micro-resonators is more fully discussed inconjunction with FIG. 5 below.

Another presently preferred method of forming resonators on the chipscale exploits the same technology of photonic crystals as is used tocreate the superprisms. Optically thin dielectric slabs, in which afully etched-through two-dimensional patterning is applied, are used toform high-Q optical cavities with modal volumes approaching thetheoretical limit of a cubic half-wavelength. Resonant cavities areformed from local defect regions within the photonic lattice. Heat cantune the resonant cavities. If the dielectric has been suitably dopedwith electo-optical polymers, the resonant cavities can be tuned byelectric fields suitably adjusting the refractive index of thedielectric. This effect is further discussed in conjunction with FIGS. 4a and 4 b below.

Employing either micro-ring resonators or photonic crystals, the passivede-multiplexers 112 convey the distinct wavelengths of optical signalsinto the resonator 140. Each resonator is programmed to capture onlyphotons of a programmed wavelength. Other wavelength photons passthrough moving from one resonator to the next in a path known as a“shuttle interconnect.” The resonators act as small “whisperinggalleries” by capturing only photons of the programmed wavelength fromthe inbound light signals. Resonators collect the information thephotons carry and then conduct the photons. By means of waveguides outof the resonator 140 to the programmed output point at the correspondingdigital signal multiplexer 188. Where each of the designated channelsfor conveying information has a programmed resonator, the incomingsignals should be appropriately routed, leaving no remaining ambientlight energy.

The analog beam steering device 160 has a distinct strategy forprogrammable routing. Rather than resonant cavities, the beam steeringdevice 160 exploits programmable superprisms as “pitchers” and“catchers.” Just as the digital resonator 140 receives the distinctwavelength beams of light at distinct spots from passive de-multiplexers112, the analog beam steering device 160 similarly receives the beamsfrom the passive de-multiplexers 115. At each of the designatedreception ports, an active or semi-active deflector 162 receives thebeam. In the analogy to a pitcher, the deflector stands ready to directthe beam at a programmed point. The deflector 162 suitably is a photoniccrystal or a pair of photonic crystals where at least one crystal isactive. The pitcher deflector 162 is programmed to aim at one of several“catcher” deflectors 164. Like the pitcher deflector 162 from which itreceives the beam, the “catcher” deflector 164 is programmed toappropriately face the “pitcher” reflector 162, and to relay the beam tothe programmed analog signal multiplexer 185 corresponding with theprogrammed output port. The pitcher reflectors 162 are programmed as towhich catcher deflectors 164 to choose while the catchers deflectors 164are simultaneously programmed to face the pitcher reflectors 162 and torelay to the multiplexer 185. Because the beams pass one to the otherwithout interference, the signal safely reaches its programmed outputmultiplexer 185.

The deflectors, 162 and 164, are suitably superprisms capable ofsteering beams. The simplest means of programming the pitchingreflectors 162 and the catching deflectors 164, is to heat thesuperprism, thereby changing its dimensions. While effective, heatingmay be less predictable without a cooling airflow. For this reason,electro-optic polymers have been used to programmably steer the beams.One of the simplest alternate approaches for using electro-optic organicmolecules within photonic crystals includes filling voids in holes thatdefine the photonic crystals. Altering the refractive index of thepolymer either optically or electrostatically indirectly tunes theeffective cavity length. This effect can be used to modulate an incidentlight beam. Even more efficient electro-optic switching is expected ifthe nanocavity design is optimized to include a void at the center ofthe cavity to place the back-filled electro-optic polymer within thefield maximum of the optical standing wave.

Another opportunity for inclusion of electro-optic molecules withinphotonic crystals relies on tuning the dispersive performance ofphotonic bandgaps. The relatively flat band structure exhibited byphotonic crystals in certain directions leads to a large density ofstates and results in lensing and superprism effects. These effects canlead to electro-optically controlled or steered collimated beams thatwill serve as wavelength selective beam steerers.

Chip scale steering is enabled by the use of III-V on Silicon,silicon-on-insulator (SOI), and electro-optic polymer technology intocompelling wavelength selective devices that enable rapidlyreconfigurable wavelength selective routers. Devices that in oneembodiment may entail III-V gain or electro-optic polymers for use inwavelength selective routers include: (1) electrically pumped photoniccrystal micro resonator lasers or gain elements with similarlithographic control and electro-optic polymer tuning; (2) electricallypumped ring or micro disk lasers whose output wavelength is controllablevia lithography and potentially tunable through the use of anelectro-optic polymer; (3) resonant defect coupled photonic crystalwaveguides, also using electo-optic tuning for wavelength routing; and(4) coupling structures that enable the upper layer III-V devices tocouple down to the silicon waveguides in the SOI interconnect layer.

Referring now to FIG. 3, a large bandgap is associated with a triangularsuperprism 200. This geometry is more completely described in thediagram showing the significant dimensions 208. The abscissa of thenormalized frequency graph includes these dimensions 210. This geometryowes its performance to a high degree of symmetry and will focus light.

The unique properties of a square geometry differ greatly from atriangular geometry in that there exists a dimension along the diagonaldistinct from the lateral dimension. The bandgap becomes very narrow.The conduction band is very flat. Iso-frequency contours are squareallowing the light to collimated. This is the geometry of a photoniccrystal resonator. In short, photons of these wavelengths pass throughthe square lattice. But, light of the appropriate bandgap willcollimate, resulting in a photonic crystal resonator.

Referring now to FIG. 4 a, a defect 232 is placed in the triangulargeometry of a superprism 200 generates similar effects. Rather than theregular repetition of the triangular lattice, the expected hole at 232is absent, hence the defect. Two effects take over. Total internalreflection and Bragg diffraction, i.e. constructive multiple-beaminterference in the periodic structure which can expel light from thematerial for certain frequencies and directions of incidence are thebase phenomenon for photonic crystals.

Referring not now to FIG. 4 b, to enhance the effect, additional defectsare inserted, e.g. 234 and 236, to act as photonic crystal mirrors.

Referring now to FIGS. 5 and 6, construction of a microresonator 240 isexplained. A compound semiconductor structure containing an opticallyactive layer is grown on top of the passive ring waveguide asillustrated in FIG. 5. The evanescent optical field of the ringwaveguide overlaps the active layer allowing interaction with theresonant optical mode via photon absorption or emission. The amount ofloss (or gain) in the resonator, and therefore its Q as well, is thendetermined by the number of photons coupled into or out of the resonantmode via the active layer. External control of the active layer emissionis achieved through electrical biasing of a p-n junction (forming alight emitting diode), or by optical pumping at an absorptive wavelengthsufficiently removed from the signal channels.

One presently preferred structure for the micro-resonator 240 is anInGaAsN QW material structure on native substrates (GaAs). A crosssection of the III-V material structure is shown in FIG. 6. A perovskiteinterfacial layer and thin III-V buffer layer are grown directly on theSi surface of the SOI wafer. A low refractive index optical isolationlayer is grown next, followed by lower carrier confinement layers thatsandwich an InGaAsN quantum well active layer. The optical isolationlayer includes an oxidized high Al mole fraction AlGaAs layer asdescribed below. The optical emitting structure may be undoped, ifintended for optical pumping, or may contain a doped p-n junctionforming an electrically pumped LED structure. In the latter case, anoptional etch stop layer may be included within the lower confinementlayer to assist in electrical contact formation.

The refractive index and thickness of layers between the passive Siwaveguide 242 and the optically active layer of a III-V stack 244 areimportant design parameters of the resonator 240 as these factorslargely determine the coupling between the two and the strength of thegain/loss control of the resonator 240. To provide optical andelectrical isolation, it is desirable to have non-conductive, lowrefraction index material between these two regions. For this, a high Almole fraction AlGaAs buffer layer is included above the heteroepitaxialinterface layer (FIG. 5), then laterally oxidized once the resonatorstructure has been defined by etching. The resulting structure of theresonator 240 can be readily produced by current chip formulationtechniques as demonstrated in the photomicrograph of FIG. 6. The samelayering forms the waveguides 242 and the stack 244.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment.

1-47. (canceled)
 48. A WDM router comprising a chip, the chip includinga programmable wavelength filter resonator for changing paths ofdifferent wavelength channels of light, and a device forcross-connecting selected wavelength to selected outputs, the resonatorincluding at least one of dynamically programmable wavelength filterphotonic crystal resonator components and dynamically programmablewavelength filter ring resonator components.
 49. The WDM router of claim48, wherein the resonator includes tunable wavelength filter ringresonator components.
 50. The WDM router of claim 49, wherein thewavelength filter ring resonator components are wavelength tunable bychanging the resonator's index to change effective cavity length. 51.The WDM router of claim 49, wherein the wavelength filter ring resonatorcomponents are EO voltage index tunable.
 52. The WDM router of claim 49,wherein the wavelength filter ring resonator components are Q-tunable byaltering optical loss within the resonator.
 53. The WDM router of claim52, wherein the wavelength filter resonator components include aQ-tunable optically active layer on top of a passive ring waveguide. 54.The WDM router of claim 48, wherein the resonator includes tunablewavelength filter photonic crystal resonator components.
 55. The WDMrouter of claim 54, wherein the resonator components include a tunablewavelength filter photonic crystal; wherein the photonic crystalincludes defects made of electro-optic polymers; and wherein index ofrefraction of a defect is changed by subjecting the electro-opticalpolymer to an electrical voltage, whereby the wavelength filterresonator is dynamically programmable.
 56. The WDM router of claim 55,wherein the wavelength filter resonator includes a photonic crystalresonator having tuned wavelength filter resonant cavities in opticallythin slabs.
 57. The WDM router of claim 54, wherein the wavelengthfilter photonic crystal resonator components are wavelength tunable bychanging index of photonic crystal defect to change effective cavitylength.
 58. The WDM router of claim 48, wherein the cross-connect deviceroutes outputs of the resonator according to wavelength and programmableelectronic inputs.
 59. The WDM router of claim 48, wherein thecross-connect device includes a passive superprism.
 60. The WDM routerof claim 48, wherein the resonator is programmable to correct for minorimperfections and to allow control of resonator characteristics.